After analysing the system's requirements we decided to implement the main server using a web service.

This web service is the system's main service, which means that will provide an Application Programming Interface (\emph{API}) or 
\emph{Web API} for the rest of the applications in this system, such as Android application and Web site. This \emph{API} has to 
implement all the functions the Android program and the Web site requires that have to do with the database.

It is decided to use a web service because it will be called from different environments. The web services provide a high 
compatibility with any system. The reason for this is that these remote calls are serialized in \emph{XML}, transferred over \emph{HTTP} 
using \emph{SOAP} protocol.

The client accesses a \emph{Web Services Description Language (WSLD)} file that specifies where is the web service, the web service's 
available functions, the parameters of this functions and the return types. Using this information the client creates an \emph{XML} 
file (\emph{SOAP} message) where function's name and parameters are serialized following the \emph{SOAP} protocol. This message is sent 
via \emph{HTTP} to the server, which is going to deserialize it, run the right method and answer the client, using the same system. In our case 
these methods are going to work on the database.